This invention generally relates to voltage regulator circuits and more specifically to voltage regulator circuits using solid-state components as series voltage regulating elements.
In recent years many battery-operated electronic devices have appeared on the marketplace. Some of these electronic devices require a voltage regulator to control the voltage supplied to various circuits so that they operate properly. Typically, a regulator comprises a series regulating element, a reference element, a comparison element, and a control element. The comparison element compares the reference voltage from the reference element to the regulated output voltage and provides an error signal corresponding to any difference between the two. The control element responds to the error signal by controlling the series regulating element to minimize the error signal.
Zener diodes are commonly used as reference elements. They maintain a fairly constant reference voltage level. However, a zener diode normally draws a minimum specified current, normally about 20 milliamperes. This is unduly wasteful for use with a load device that itself requires only a fraction as much current, particularly when the power source is a small battery which can supply only a fixed amount of energy.
The comparison and control elements may also require considerable current to operate properly. This further introduces an unnecessary energy requirement on the relatively small, fixed amount available from the battery.
Both vacuum tubes and transistors serve as the series regulating element in voltage regulators. Vacuum tubes require that the unregulated voltage be kept significantly higher than the regulated voltage in order to keep the tube conducting. Even with transistors, it is necessary to maintain a one-half volt or greater potential between the emitter electrode and the base and collector electrodes. This is normally accomplished by coupling the base electrode to the collector electrode which normally connects to the unregulated d-c power source potential. If this potential on the base-emitter junction and emitter-collector circuit is not maintained, transistors stop conducting. In circuits using batteries as the d-c power source, this requirement can foreshorten the effective battery life because a battery must then be replaced considerably before its useful output voltage is reduced to the regulated voltage (i.e., when its voltage is still 0.6 volt above the regulated voltage.)
Therefore, it is an object of this invention to provide a series voltage regulator which is especially adapted for use in battery-operated circuits.
Another object of this invention is to provide a voltage regulator in which a minimum voltage appearing across a series regulating element is reduced.
Still another object of this invention is to provide a voltage regulator in which the energy for operating the reference, comparison and control circuits is significantly reduced.